This invention relates to an angular rate sensor assembly for use in navigation equipment and, more particularly, to such a sensor assembly which has a low profile and improved mechanical stability. U.S. Pat. No. 4,621,529, the contents of which are hereby incorporated by reference, discloses an angular rate sensor assembly which includes a gyroscopic element having a spin axis, and a flexure hinge for resiliently mounting the gyroscopic element to a base. The sensor assembly further includes a torque sensing assembly which has a piezoelectric beam mounted in coaxial relation to the spin axis. A first beam restraining member mounts a first edge portion of the piezoelectric beam to the gyroscopic element and a second beam restraining member mounts an opposite edge portion of the piezoelectric beam to the base. The piezoelectric beam is adapted to generate an electrical signal proportional to the angular velocity of the sensor assembly about an axis perpendicular to the spin axis.
U.S. Pat. No. 4,715,227, the contents of which are hereby incorporated by reference, discloses an angular rate sensor assembly which is an improvement over the sensor assembly disclosed in the referenced U.S. Pat. No. 4,621,529. In the improved sensor assembly, the piezoelectric beam is generally diamond-shaped and is fixed to both the gyroscopic element and the base by means of wires oriented orthogonally both to the axis of the flexure hinge and to the spin axis.
While the assemblies disclosed in the referenced patents operate generally satisfactorily, certain improvements thereto have been found to be desirable. For example, in the previously disclosed assemblies, the piezoelectric beam is oriented colinear to the spin axis. A reduction in the axial length of the sensor assembly by positioning the piezoelectric beam in a plane perpendicular to the spin axis would reduce the overall axial length of the assembly. It is therefore an object of the present invention to provide an angular rate sensor assembly of the type disclosed in the referenced patents which has the piezoelectric beam supported in a plane perpendicular to the spin axis so that the axial length of the sensor assembly is reduced.
It is another object of this invention to provide an angular rate sensor assembly with improved mechanical stability.
It is a further object of the present invention to provide an angular rate sensor assembly of the type described wherein the gyroscopic element has increased inertial mass.
It is yet another object of the present invention to provide an angular rate sensor assembly of the type described wherein the coupling of the piezoelectric beam is selectively compliant to isolate the beam from motion in its plane. Such motion includes, for example, thermal stresses from expansion/contraction of dissimilar materials and inertial loads causing spurious stresses not proportional to the desired rate output.